U.S. patent number 10,018,951 [Application Number 15/472,572] was granted by the patent office on 2018-07-10 for image forming apparatus with controllable velocity ratio between image and developer bearing members.
This patent grant is currently assigned to Canon Kabushiki Kaisha. The grantee listed for this patent is CANON KABUSHIKI KAISHA. Invention is credited to Hisashi Nakahara, Tohru Saito, Go Shindo, Akihiko Uchiyama.
United States Patent |
10,018,951 |
Saito , et al. |
July 10, 2018 |
Image forming apparatus with controllable velocity ratio between
image and developer bearing members
Abstract
A control portion has a conversion portion that converts image
data to be used for forming a recorded image by using either a
first conversion condition which has been set such as to obtain a
first gradation characteristic in the image to be formed on the
recording material when a first image forming operation is executed
or a second conversion condition which has been set such as to
obtain a second gradation characteristic, which is different from
the first gradation characteristic, in the image when a second
image forming operation is executed, a peripheral velocity ratio
between an image bearing member and a developer bearing member
being larger during the second image forming operation than during
the first image forming operation, and enables the first image
forming operation or the second image forming operation to be
performed on the basis of converted image data.
Inventors: |
Saito; Tohru (Mishima,
JP), Uchiyama; Akihiko (Mishima, JP),
Nakahara; Hisashi (Numazu, JP), Shindo; Go
(Mishima, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
CANON KABUSHIKI KAISHA |
Tokyo |
N/A |
JP |
|
|
Assignee: |
Canon Kabushiki Kaisha (Tokyo,
JP)
|
Family
ID: |
59960927 |
Appl.
No.: |
15/472,572 |
Filed: |
March 29, 2017 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20170285546 A1 |
Oct 5, 2017 |
|
Foreign Application Priority Data
|
|
|
|
|
Mar 31, 2016 [JP] |
|
|
2016-072514 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G03G
15/5008 (20130101); G03G 15/5087 (20130101); G03G
15/5062 (20130101); G03G 15/0806 (20130101); G03G
15/55 (20130101); G03G 2221/1657 (20130101) |
Current International
Class: |
G03G
15/00 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
08-227222 |
|
Sep 1996 |
|
JP |
|
2013-114252 |
|
Jun 2013 |
|
JP |
|
2013-210489 |
|
Oct 2013 |
|
JP |
|
Other References
US. Appl. No. 15/459,384, filed Mar. 15, 2017, Hisashi Nakahra,
Akihiko Uchiyama. cited by applicant.
|
Primary Examiner: Brase; Sandra
Attorney, Agent or Firm: Fitzpatrick, Cella, Harper &
Scinto
Claims
What is claimed is:
1. An image forming apparatus comprising: an image bearing member
on which an electrostatic image is formed; a developer bearing
member that develops the electrostatic image, which has been formed
on the image bearing member, with a developer; and a control
portion that controls the image bearing member and the developer
bearing member so as to enable execution of a first image forming
operation by which a recorded image is formed by rotating the image
bearing member and the developer bearing member at a first
peripheral velocity ratio and a second image forming operation by
which a recorded image is formed by rotating the image bearing
member and the developer bearing member at a second peripheral
velocity ratio which is greater than the first peripheral velocity
ratio, where the peripheral velocity ratio is defined as a ratio of
a peripheral velocity of the developer bearing member to a
peripheral velocity of the image bearing member, wherein the
control portion: has a conversion portion that converts image data,
which are used for forming the recorded image, by using either a
first conversion condition which has been set so as to obtain a
first gradation characteristic in the recorded image when the first
image forming operation is executed or a second conversion
condition which has been set so as to obtain a second gradation
characteristic, which is different from the first gradation
characteristic, in the recorded image when the second image forming
operation is executed, and enables the first image forming
operation or the second image forming operation to be performed on
the basis of image data converted by the conversion portion.
2. The image forming apparatus according to claim 1, wherein the
second gradation characteristic is a gradation characteristic which
is the same as the first gradation characteristic in a first
density region in the recorded image and is a gradation
characteristic such that a density increase rate gradually
increases in a second density region where density is higher than
in the first density region.
3. The image forming apparatus according to claim 1, wherein in the
first gradation characteristic, a density increase rate is constant
over the entire density range in the recorded image.
4. The image forming apparatus according to claim 1, wherein the
control portion executes the first image forming operation when
only dot data with a density less than a predetermined threshold
are included in the image data to be converted in the conversion
portion; and the conversion portion converts the image data by
using the first conversion condition during the first image forming
operation.
5. The image forming apparatus according to claim 4, wherein the
control portion executes the second image forming operation when
dot data with a density of at least the predetermined threshold are
included in the image data to be converted in the conversion
portion; and the conversion portion converts the image data by
using the second conversion condition during the second image
forming operation.
6. The image forming apparatus according to claim 5, wherein the
execution of either of the first image forming operation and the
second image forming operation is designatable.
7. The image forming apparatus according to claim 6, wherein the
control portion executes the first image forming operation when
only dot data with a density less than the predetermined threshold
are included in the image data, even when the execution of the
second image forming operation is designated.
8. The image forming apparatus according to claim 1, wherein the
conversion portion converts the image data by gamma correction.
9. The image forming apparatus according to claim 1, wherein a
laid-on level of the developer per unit area of the recording
material in the recorded image in the second image forming
operation is greater than the laid-on level in the first image
forming operation.
10. The image forming apparatus according to claim 1, wherein a
peripheral velocity of the image bearing member in the second image
forming operation is lower than the peripheral velocity of the
image bearing member in the first image forming operation.
11. The image forming apparatus according to claim 1, wherein the
second peripheral velocity ratio is set such that a laid-on level
of the developer per unit area of the recording material in the
recorded image at the second peripheral velocity ratio is larger
than that at the first peripheral velocity ratio.
12. The image forming apparatus according to claim 1, further
comprising an exposure portion for exposing a surface of the image
bearing member to form an electrostatic image on the surface; a
transfer portion for transferring a developer image borne by the
image bearing member to the recording material; and a fixing
portion for fixing the developer image to the recording
material.
13. An image forming apparatus comprising: an image bearing member
on which an electrostatic image is formed; a developer bearing
member that develops the electrostatic image, which has been formed
on the image bearing member, with a developer; and a control
portion that controls the image bearing member and the developer
bearing member so as to enable execution of a first image forming
operation by which a recorded image is formed by rotating the image
bearing member and the developer bearing member at a first
peripheral velocity ratio and a second image forming operation by
which a recorded image is formed by rotating the image bearing
member and the developer bearing member at a second peripheral
velocity ratio which is greater than the first peripheral velocity
ratio, where the peripheral velocity ratio is defined as a ratio of
a peripheral velocity of the developer bearing member to a
peripheral velocity of the image bearing member, wherein the
control portion: has a conversion portion that converts image data,
which are used for forming the recorded image, by using either a
first conversion condition for outputting the recorded image in a
first color reproduction range when the first image forming
operation is executed or a second conversion condition for
outputting the recorded image in a second color reproduction range,
which is wider than the first color reproduction range, when the
second image forming operation is executed, and enables the first
image forming operation or the second image forming operation to be
performed on the basis of image data converted by the conversion
portion.
14. The image forming apparatus according to claim 13, wherein the
conversion of the image data performed by the conversion portion is
a color matching conversion for matching tinges between an image
displayed by an image display device that displays an image on the
basis of image data before the conversion, and an image formed on a
recording material on the basis of image data after the
conversion.
15. The image forming apparatus according to claim 13, wherein a
laid-on level of the developer per unit area of the recording
material in the recorded image in the second image forming
operation is greater than the laid-on level in the first image
forming operation.
16. The image forming apparatus according to claim 13, wherein a
peripheral velocity of the image bearing member in the second image
forming operation is lower than the peripheral velocity of the
image bearing member in the first image forming operation.
17. The image forming apparatus according to claim 13, wherein the
second peripheral velocity ratio is set such that a laid-on level
of the developer per unit area of the recording material in the
recorded image at the second peripheral velocity ratio is larger
than that at the first peripheral velocity ratio.
18. The image forming apparatus according to claim 13, further
comprising an exposure portion for exposing a surface of the image
bearing member to form an electrostatic image on the surface; a
transfer portion for transferring a developer image borne by the
image bearing member to the recording material; and a fixing
portion for fixing the developer image to the recording material.
Description
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to an image forming apparatus using
an electrophotographic method.
Description of the Related Art
In recent years, in an image forming apparatus in which a color
image is formed on a recording material by using an
electrophotographic method, such as a color laser printer, color
gamut has become important as one of high image quality indexes of
the output image. The color gamut represents a color reproduction
range that can be reproduced by the image forming apparatus, and a
wider color gamut corresponds to a wider color reproduction range.
As a method of enlarging the color gamut, for example, in a color
image forming apparatus, dense Y, dense M, and dense C developers
are used in addition to developers of four colors Y, M, C and K
that are usually used, and a wide color gamut is realized by using
developers with more than four colors.
As another method, it is conceivable to increase the color gamut of
the output image fixed to the recording material to above the usual
level by increasing the amount of developer (referred to
hereinbelow as "toner amount") placed on the recording material to
above the usual level. Further, as a method for changing the toner
amount, it is conceivable to change the peripheral velocity ratio
of a photosensitive drum as an image bearing member and a
developing roller as a developer bearing member. As a method for
changing the peripheral velocity ratio of the photosensitive drum
and the developing roller, Japanese Patent Application Publication
No. H8-227222 suggests a method for adjusting the tinge of the
secondary color (red color) by changing the rotation speed of the
developing roller. Further, Japanese Patent Application Publication
No. 2013-210489 suggests a method for improving image graininess,
that is, reducing toner scattering and image blurring, by reducing
the rotation speed of the photosensitive drum.
SUMMARY OF THE INVENTION
However, the following problems are associated with the
abovementioned conventional examples. With the method using
developers of more than four colors by adding dense Y, dense M, and
dense C developers, the number of image forming units increases
correspondingly to the increase in the number of developers, and
therefore, the image forming apparatus becomes larger. Further, the
objective of the method disclosed in Japanese Patent Application
Publication No. 2013-210489 in which the peripheral velocity of the
photosensitive drum is made to be different from the peripheral
velocity of the developing roller is to adjust the tinge and
improve the image graininess, and it is not always possible to
expand the color gamut advantageously. That is, with the methods
disclosed in Japanese Patent Application Publication Nos. H8-227222
and 2013-210489, an image having an unnatural tinge is sometimes
obtained.
It is an objective of the present invention to provide a technique
capable of reducing an unnatural tinge.
In order to achieve the abovementioned objective, the image forming
apparatus of the present invention is an image forming apparatus
comprising:
an image bearing member on which an electrostatic image is
formed;
a developer bearing member that develops the electrostatic image,
which has been formed on the image bearing member, with a
developer; and
a control portion that controls the image bearing member and the
developer bearing member such as to enable execution of a first
image forming operation by which a recorded image is formed by
rotating the image bearing member and the developer bearing member
at a first peripheral velocity ratio and a second image forming
operation by which a recorded image is formed by rotating the image
bearing member and the developer bearing member at a second
peripheral velocity ratio which is greater than the first
peripheral velocity ratio, where the peripheral velocity ratio is
defined as a ratio of a peripheral velocity of the developer
bearing member to a peripheral velocity of the image bearing
member, wherein
the control portion
has a conversion portion that converts image data, which are used
for forming the recorded image, by using either a first conversion
condition which has been set such as to obtain a first gradation
characteristic in the recorded image when the first image forming
operation is executed or a second conversion condition which has
been set such as to obtain a second gradation characteristic, which
is different from the first gradation characteristic, in the
recorded image when the second image forming operation is executed,
and
enables the first image forming operation or the second image
forming operation to be performed on the basis of image data
converted by the conversion portion.
In order to achieve the abovementioned objective, the image forming
apparatus of the present invention is an image forming apparatus
comprising:
an image bearing member on which an electrostatic image is
formed;
a developer bearing member that develops the electrostatic image,
which has been formed on the image bearing member, with a
developer; and
a control portion that controls the image bearing member and the
developer bearing member such as to enable execution of a first
image forming operation by which a recorded image is formed by
rotating the image bearing member and the developer bearing member
at a first peripheral velocity ratio and a second image forming
operation by which a recorded image is formed by rotating the image
bearing member and the developer bearing member at a second
peripheral velocity ratio which is greater than the first
peripheral velocity ratio, where the peripheral velocity ratio is
defined as a ratio of a peripheral velocity of the developer
bearing member to a peripheral velocity of the image bearing
member, wherein
the control portion
has a conversion portion that converts image data, which are used
for forming the recorded image, by using either a first conversion
condition for outputting the recorded image in a first color
reproduction range when the first image forming operation is
executed or a second conversion condition for outputting the
recorded image in a second color reproduction range, which is wider
than the first color reproduction range, when the second image
forming operation is executed, and
enables the first image forming operation or the second image
forming operation to be performed on the basis of image data
converted by the conversion portion.
According to the present invention, it is possible to reduce the
occurrence of an unnatural tinge.
Further features of the present invention will become apparent from
the following description of exemplary embodiments with reference
to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a flowchart of the image processing operation in Example
1 of the present invention;
FIG. 2 is a schematic cross-sectional view of the image forming
apparatus according to Example 1 of the present invention;
FIG. 3 is a cross-sectional view of the process cartridge in
Example 1 of the present invention;
FIG. 4 is a graph showing the relationship between the peripheral
velocity ratio and the toner amount per unit surface area of the
photosensitive drum;
FIG. 5 is a graph showing the relationship between the amount of
toner per unit surface area on a recording material and a
reflection density;
FIG. 6 is a block diagram of a control configuration of the image
forming apparatus according to Example 1 of the present
invention;
FIG. 7 is an explanatory drawing illustrating .gamma. correction in
the normal image forming mode in Example 1 of the present
invention;
FIG. 8 is an explanatory drawing illustrating the case where
.gamma. correction of the normal image forming mode is performed in
the wide color gamut image forming mode;
FIG. 9 is an explanatory drawing illustrating y correction in the
wide color gamut image forming mode according in Example 1 of the
present invention;
FIG. 10 is a chromaticity diagram in Example 1 of the present
invention;
FIG. 11 is an explanatory drawing illustrating color matching
conversion in the normal image forming mode;
FIG. 12 is an explanatory drawing illustrating color matching
conversion in the wide image forming mode;
FIG. 13 is a flowchart of image forming mode selection in Example 3
of the present invention;
FIG. 14 is a flowchart of the image processing operation in the
conventional example;
and
FIG. 15 is a schematic diagram of a drive coupling configuration in
an example of the present invention.
DESCRIPTION OF THE EMBODIMENTS
Hereinafter, a description will be given, with reference to the
drawings, of embodiments (examples) of the present invention.
However, the sizes, materials, shapes, their relative arrangements,
or the like of constituents described in the embodiments may be
appropriately changed according to the configurations, various
conditions, or the like of apparatuses to which the invention is
applied. Therefore, the sizes, materials, shapes, their relative
arrangements, or the like of the constituents described in the
embodiments do not intend to limit the scope of the invention to
the following embodiments.
EXAMPLE 1
Examples of the image forming apparatus to which the present
invention is applied include a copier, a laser beam printer (LBP),
a printer, a facsimile machine, a microfilm reader/printer, and a
recorder using an electrophotographic image forming process. In
these image forming apparatuses, an unfixed toner image of target
image information, which has been formed and borne on a recording
material (transfer material, printing paper, photosensitive paper,
glossy paper, OHT, electrostatic recording paper, etc.) by an
intermediate transfer method or a direct transfer method in an
image producing process portion is fixed as a fixed image.
The image forming apparatus according to the present example has
two image forming modes, namely, a normal image forming mode in
which a normal image density is obtained as a first image forming
operation and a wide color gamut image forming mode in which a wide
color gamut image can be reproduced as a second image forming
operation. The first image forming operation and the second image
forming operation are controlled in an executable manner by a
control portion. In the wide color gamut image forming mode, the
peripheral velocity ratio of the photosensitive drum as an image
bearing member and the developing roller as a developer bearing
member, that is, the ratio of the peripheral velocity of the
developing roller to the peripheral velocity of the photosensitive
drum, is changed. Therefore, the peripheral velocity ratio of the
photosensitive drum and the developing roller differs between the
image forming modes. In the present example, the first image
forming operation is the normal image forming mode and the second
image forming operation is the wide color gamut image forming mode,
but the present invention is not limited thereto. When two kinds of
normal image density are set, the first image forming operation is
the first normal image forming mode and the second image forming
operation is the second normal image forming mode.
A specific feature of the present example is that different image
formation conditions are used in the normal image forming mode and
the wide color gamut image forming mode. Here, using different
image formation conditions means, for example, that specifications
of processing in various types of image processing such as color
matching, color separation, .gamma. correction, and halftoning,
that is, conversion conditions (processing conditions) between
original image data (first image data) and image data after
processing (second image data), are changed. In Example 1, the case
is described in which different .gamma. corrections (first .gamma.
correction and second .gamma. correction) suitable for the
respective modes are performed as the image formation conditions in
the normal image forming mode and the wide color gamut image
forming mode.
FIG. 1 is a flowchart showing the flow of the image processing
operation in the example. As shown in FIG. 1, in the present
example, image formation conditions to be used in the normal image
forming mode and the wide color gamut image forming mode are
changed.
FIG. 14 is a flowchart showing the flow of the image forming
process in the conventional example. As shown in FIG. 14, in the
conventional example, image formation conditions used in the normal
image forming mode and the wide color gamut image forming mode are
the same.
(Image Forming Apparatus)
FIG. 2 is a schematic cross-sectional view of an image forming
apparatus 200 according to an example of the present invention. The
image forming apparatus 200 of the present example is a full-color
laser printer using an in-line method and an intermediate transfer
method. The image forming apparatus 200 can form a full color image
on a recording material (for example, recording paper such as plain
paper) according to image information. The image information is
sent to the image forming apparatus 200 from an image reading
device connected to the image forming apparatus 200, or a host PC
(not shown in the drawing) such as a personal computer communicably
connected to the image forming apparatus 200. The sent image
information is inputted to an engine controller 603 as a control
portion having a CPU 214 or a memory located in the image forming
apparatus 200, or to a video controller 602 as a conversion
portion. Various operations including the image forming operation
in the image forming apparatus 200 are controlled by the engine
controller 603 as a control portion.
The image forming apparatus 200 includes, as a plurality of image
forming portions, first, second, third, and fourth image forming
portions SY, SM, SC, and SK for forming images of yellow (Y),
magenta (M), cyan (C), and black (K) colors, respectively. Here,
the image forming portion (or image forming station) is configured
of a process cartridge 208 and a primary transfer roller 212
disposed to face the process cartridge, with an intermediate
transfer belt 205 being interposed therebetween. In the present
example, the first to fourth image forming portions SY, SM, SC, and
SK are disposed in a row in a direction intersecting the vertical
direction and the horizontal direction. In the present example, the
first to fourth image forming portions have substantially the same
configuration and operation, except for the color of the image to
be formed. Therefore, in the following general description, the
suffixes Y, M, C, and K assigned to the code for indicating that an
element is provided for a specific color are omitted, in
particular, when no distinction is required. Such a configuration
is, however, not limiting. For example, the image forming portion
itself may be made large by increasing the capacity of black
(K).
The image forming apparatus 200 includes, as a plurality of image
carriers, four drum-shaped electrophotographic photosensitive
members, that is, photosensitive drums 201, arranged side by side
in a direction intersecting the vertical direction and the
horizontal direction. The photosensitive drum 201 is rotationally
driven by driving means (driving source) (not shown in the drawing)
in the direction of an arrow A (clockwise direction) in the
drawing. A charging roller 202 and a scanner unit (exposure device)
203 are disposed on the periphery of the photosensitive drum 201.
The charging roller 202 is charging means for uniformly charging
the surface of the photosensitive drum 201. The scanner unit 203 is
an exposure portion that forms an electrostatic image
(electrostatic latent image) on the photosensitive drum 201 by
irradiation with a laser beam on the basis of image information. A
developing unit (developing device) 204, a cleaning blade 206, and
a pre-exposure LED 216 are also disposed on the periphery of the
photosensitive drum 201. The developing unit 204 is developing
means for developing the electrostatic image as a toner image
(developer image). The cleaning blade 206 is cleaning means for
removing the toner (untransferred toner) remaining on the surface
of the photosensitive drum 201 after the transfer. The pre-exposure
LED 216 is static eliminating means for neutralizing the potential
on the photosensitive drum 201.
An intermediate transfer belt 205 as an intermediate transfer
member for transferring a toner image as a developer image on the
photosensitive drum 201 to a recording material 207 is disposed so
as to face the four photosensitive drums 201. The photosensitive
drums 201, the charging roller 202 as charging process means of the
photosensitive drum 201, the developing unit 204, and the cleaning
blade 206 are integrally configured in the process cartridge 208.
The process cartridge 208 is detachably attachable to the apparatus
main body of the image forming apparatus 200. The apparatus main
body, as referred to herein, indicates constituent parts of the
image forming apparatus 200 excluding the process cartridge 208. In
the present example, the process cartridges 208 for the respective
colors have the same shape, and toners of yellow (Y), magenta (M),
cyan (C), and black (K) colors are accommodated in the process
cartridges 208 for the respective colors. Further, the toner in the
present example has a negative charging characteristic.
The intermediate transfer belt 205 formed of an endless belt as an
intermediate transfer member comes into contact with all of the
photosensitive drums 201 and rotates in the direction of an arrow B
(counterclockwise direction) in the drawing. The intermediate
transfer belt 205 is wound around a driving roller 209, a secondary
transfer opposing roller 210, and a driven roller 211 as a
plurality of support members. On the inner peripheral surface side
of the intermediate transfer belt 205, four primary transfer
rollers 212 are disposed side by side as primary transfer portion
so as to face the respective photosensitive drums 201. Further, a
bias having a polarity opposite to the regular charging polarity
(as described above, negative polarity in the present example) of
the toner is applied from a primary transfer bias power source (not
shown in the drawing) to the primary transfer roller 212. As a
result, the toner image on the photosensitive drum 201 is
transferred onto the intermediate transfer belt 205. Further, a
secondary transfer roller 213 is disposed as secondary transfer
portion at a position facing the secondary transfer opposing roller
210 on the outer peripheral surface side of the intermediate
transfer belt 205. A bias having a polarity opposite to the regular
charging polarity of the toner is applied from a secondary transfer
bias power supply (not shown in the drawing) to the secondary
transfer roller 213. As a result, the toner image on the
intermediate transfer belt 205 is transferred onto the recording
material 207. The toner image is then heated and fixed by a fixing
device 220 as a fixing portion disposed on the downstream side,
whereby the toner image is fixed as a fixed image on the recording
material 207.
(Process Cartridge)
FIG. 3 is a schematic cross-sectional view of the process cartridge
208 of the present example as seen from the longitudinal direction
(rotational axis direction) of the photosensitive drum 201. In the
present example, the configuration and operation of the process
cartridges 208 for each color are the same except for the type
(color) of the developer accommodated therein, and FIG. 3 shows, by
way of example, the process cartridge for yellow (Y) color. The
process cartridge 208 includes a photosensitive member unit 301
having a photosensitive drum 201, or the like, as an image bearing
member, and a developing unit 204 having a developing roller 302 or
the like. The photosensitive member unit 301 has a cleaning frame
303 as a frame that supports various elements in the photosensitive
member unit 301. The photosensitive drum 201 is rotatably attached
to the cleaning frame 303 through a bearing (not shown in the
drawing). The photosensitive drum 201 is rotationally driven in the
direction of an arrow A (clockwise direction) in the drawing in
accordance with the image forming operation by transmitting the
driving force of the below-described driving motor as driving
portion (driving source) to the photosensitive member unit 301. The
photosensitive drum 201, which is the principal component of the
image forming process, uses an organic photosensitive drum in which
an undercoat layer which is a functional film, a carrier generating
layer, and a carrier transfer layer are sequentially coated on the
outer peripheral surface of an aluminum cylinder. Further, in the
photosensitive member unit 301, the cleaning member 206 and the
charging roller 202 are disposed so as to be in contact with the
peripheral surface of the photosensitive drum 201. The
untransferred toner removed from the surface of the photosensitive
drum 201 by the cleaning member 206 falls down and is accommodated
in the cleaning frame 303.
The charging roller 202 serving as charging portion is driven to
rotate by pressing a roller portion made from an electrically
conductive rubber into contact with the photosensitive drum 201 as
an image bearing member. Here, in the core metal of the charging
roller 202, as a charging step, a predetermined DC voltage is
applied as a charging bias to the photosensitive drum 201 from a
charging voltage application portion (high-voltage power source)
401 as charging roller bias application means. As a result, a
uniform dark potential (Vd) is formed on the surface of the
photosensitive drum 201. The aforementioned scanner unit 203
exposes the photosensitive drum 201 by a laser beam L emitted
correspondingly to the image data. Electric charges on the surface
in the exposed photosensitive drum 201 are eliminated by the
carriers from the carrier generating layer, and the electric
potential decreases. As a result, an electrostatic latent image
with a predetermined light potential (Vl) at the exposed segment
and a predetermined dark potential (Vd) at the unexposed segment is
formed on the photosensitive drum 201.
The developing unit 204 has a developing roller 302 (rotation
direction is indicated by an arrow D) as a developer bearing
member, a developing blade 308, a toner supply roller 304 (rotation
direction is indicated by an arrow E), a toner 305, a toner
accommodating chamber 306 that accommodates the toner 305, and an
agitating member 307. The toner accommodating chamber 306 has a
developing chamber 18a and a developer accommodating chamber 18b.
The developer accommodating chamber 18b is disposed below the
developing chamber 18a and communicates with the developing chamber
18a via a communication port provided above the developer
accommodating chamber 18b. The toner 305 is moved in the toner
accommodating chamber 306 by the movement (rotation direction is
indicated by an arrow G) of the agitating member 307 as a developer
transport member. In the present example, as described above, a
toner having a negative polarity as a regular charge polarity is
used as toner 305, and the following explanation is based on the
case of using a negative-charging toner. However, the toner that
can be used in the present invention is not limited to the
negative-charging toner, and depending on the apparatus
configuration, a toner having a positive polarity as a regular
charge polarity may be used.
The developing roller 302 as a developer bearing member that is in
contact with the photosensitive drum 201 as an image bearing member
and rotates in the direction indicated by an arrow D in the drawing
by receiving a driving force of a driving motor 52 or a driving
motor 53 shown in FIG. 15 as driving portion is provided in the
developing chamber 18a. In the present example, the developing
roller 302 and the photosensitive drum 201 rotate such that the
surfaces thereof move in the same direction in an opposing portion
(contact portion C1) which is a segment where the toner 305 carried
by the developing roller 302 is supplied to the photosensitive drum
201. Further, a predetermined DC bias (developing bias) sufficient
to develop and visualize the electrostatic latent image on the
photosensitive drum 201 as a toner image (developer image) is
applied from a developing voltage application portion (high-voltage
power source) 402 serving as developing bias application means to
the developing roller 302. At the contact portion C1 where the
developing roller 302 and the photosensitive drum 201 are in
contact with each other, the toner is transferred only to the light
potential region from the potential difference, thereby visualizing
the electrostatic latent image. Thus, the electrostatic latent
image is an image configured of a light potential region as a first
potential region for adhering the toner and a dark potential region
as a second potential region for not adhering the toner.
A toner supply roller (referred to hereinbelow as "supply roller")
304 and a developing blade (referred to hereinbelow as "regulating
member") 308 as a toner amount regulating member are further
arranged in the developing chamber 18a. The supply roller 304 as a
developer supply member is a roller for supplying the toner 305
transported from the developer accommodating chamber 18b to the
developing roller 302. The supply roller 304 is an elastic sponge
roller in which a foam layer is formed on the outer periphery of a
conductive core metal. In the opposing portion of the supply roller
facing the developing roller 302, a predetermined contact portion
C2 (contact region) is formed where the supply roller 304 is in
contact with the peripheral surface of the developing roller 302.
The regulating member 308 regulates the coating amount of the toner
on the developing roller 302, which is supplied by the supply
roller 304, and imparts an electric charge thereto. A bias (supply
bias) is applied to the supply roller 304 from a high-voltage power
source (not shown in the drawing) serving as supply bias
application portion.
Here, the bias applied by a developing voltage application portion
402, a charging voltage application portion 401, and the supply
roller bias power source is controlled by an engine controller 603,
which is a control portion, on the basis of the information
obtained by a printing mode information acquisition portion 70. The
printing mode information acquisition portion 70 acquires
information inputted from an operation panel or a printer driver
(not shown in the drawing) of the image forming apparatus 200, or a
host PC.
As shown in FIG. 15, in the present example, the configuration of
the driving portion for driving the shafts of the photosensitive
drum 201, the developing roller 302, the agitating member 307, and
the supply roller 304 differs depending on the process cartridge
208. FIG. 15 is a schematic diagram showing a drive coupling
configuration in an example of the present invention.
Yellow (Y), magenta (M), and cyan (C) process cartridges 208 are
configured in the following manner. Thus, as shown in FIG. 15, the
driving portion for rotationally driving photosensitive drums 201Y,
201M, 201K and the driving portion for rotationally driving
developing rollers 302Y, 302M, 302K are configured to have separate
driving sources. The driving portion for rotationally driving the
photosensitive drums 201Y, 201M, 201C is configured of a driving
motor 51 and a gear train that transmits the rotational driving
force of the driving motor 51. Meanwhile, the driving portion for
rotationally driving the developing rollers 302Y, 302M, 302C is
configured of a driving motor 52 and a gear train that transmits
the rotational driving force of the driving motor 52. The driving
motor 52, together with another gear train, also constitutes
driving portion for rotationally driving the rotation shafts of
agitating members 307Y, 307M, 307C. Further, the driving motor 52,
together with still another gear train, also constitutes driving
portion for rotationally driving supply rollers 304Y, 304M,
304C.
In the black (K) process cartridge 208, driving portion for
rotationally driving the photosensitive drum 201K, driving portion
for rotationally driving the developing roller 302K, and driving
portion for rotationally driving the supply roller 304K are
configured of a common single driving motor 53. Further, the
driving motor 53, together with another gear train, constitutes
driving portion for rotationally driving the rotation shaft of the
agitating member 307K, and together with yet another gear train,
constitutes driving portion for rotationally driving a driving
roller 209 for circulatory moving the intermediate transfer belt
205. These various driving motors and gear trains correspond to
driving portion capable of rotationally driving the image bearing
member, the developer bearing member, the supply member, and the
transport member individually and variably in the present
invention, and are controlled by the engine controller 603 as a
control portion.
Conventionally, the photosensitive drum and the developing roller
are driven from the same driving source (driving motor) through a
gear train. For this reason, the peripheral velocity ratio of the
photosensitive drum and the developing roller is uniquely
determined by the gear ratio and is fixed. By contrast, in the
present example, in the YMC cartridge, the photosensitive drum and
the developing roller are driven from separate driving sources, so
that the peripheral velocity ratio of the photosensitive drum and
the developing roller can be varied.
As an example of the toner that can be used in the present example,
a substantially spherical toner is used that is produced by a
polymerization method, includes a low-softening-point substance at
5 wt % to 30 wt %, and has a shape factor SF-1 of 100 to 110
(simply referred to hereinbelow as "polymerized toner"). The
low-softening-point substance is a compound in which the main
maximum peak value measured in accordance with ASTM D 3418-8 shows
40.degree. C. to 90.degree. C. The main maximum peak temperature of
the polymerized toner is measured, for example, with DSC-7
manufactured by PerkinElmer, Inc. Temperature correction of the
apparatus detection portion uses the melting points of indium and
zinc, and the heat of fusion of indium is used for calorific value
correction. The measurements were carried out at a heating rate of
10.degree. C./min by using an aluminum pan as a sample and an empty
pan as a reference. Specifically, paraffin waxes, polyolefins,
Fischer-Tropsch wax, amide waxes, higher fatty acids, ester waxes
and derivatives thereof or graft/block compounds thereof can be
used. An ester wax is preferred that has one or more long-chain
ester moieties with ten or more carbon atoms which are represented
by the following general structural formula. The structural
formulas of representative compounds of specific ester waxes are
shown below as general structural formulas (1), (2) and (3).
##STR00001##
In the formula, a and b each represent an integer of 0 to 4, and
a+b is 4. R1 and R2 each represent an organic group with the number
of carbon atoms being an integer of 1 to 40, and the difference in
the number of carbon atoms between R1 and R2 is at least 10. n and
m each represent an integer of 0 to 15, and n and m are not 0 at
the same time.
##STR00002##
In the formula, a and b each represent an integer of 0 to 4, and
a+b is 4. R1 represents an organic group with the number of carbon
atoms being an integer of 1 to 40. n and m each represent an
integer of 0 to 15, and n and m are not 0 at the same time.
##STR00003##
In the formula, a and b each represent an integer of 0 to 3, and
a+b is not more than 3. R1 and R2 each represent an organic group
with the number of carbon atoms being an integer of 1 to 40, and
the difference in the number of carbon atoms between R1 and R2 is
at least 10. R3 represents an organic group with at least one
carbon atom. n and m each represent an integer of 0 to 15, and n
and m are not 0 at the same time.
An ester wax preferably used in the present invention has a
hardness of 0.5 to 5.0. The hardness of the ester wax is a value
obtained by preparing a cylindrical sample having a diameter of 20
mm and a thickness of 5 mm and then measuring a Vickers hardness
using a dynamic microhardness meter (DUH-200) manufactured by
Shimadzu Corporation. The Vickers hardness is determined under the
following measurement conditions: displacement of 10 .mu.m is
induced at a load speed of 9.67 mm/sec under a load of 0.5 g,
followed by holding for 15 sec and measuring the shape of the
obtained dent. The hardness of the ester wax preferably used in the
present invention has a value of 0.5 to 5.0. Examples of specific
compounds are represented by the following chemical formulas (4),
(5), (6), and (7).
##STR00004##
The shape factor SF-1, as referred to herein, is a numerical value
indicating the ratio of the spherical roundness of a spherical
substance, and is represented by a value obtained by dividing a
second power of the maximum length MAXLNG of an elliptical figure
formed by projecting the spherical substance onto a two-dimensional
plane by the AREA of the figure and multiplying by 100.pi./4. In
other words, the shape factor SF-1 is defined by the following
equation.
.times..pi..times..times..times..times..times..times..pi..times.
##EQU00001##
Calculations were performed by the equation above by randomly
sampling 100 toner images using FE-SEM (S-800), manufactured by
Hitachi, Ltd., introducing the image information via an interface
to an image analyzer (Luzex 3), manufactured by Nireco Corporation,
and analyzing the image information.
A cyan toner was prepared in the following manner. A total of 710
parts by weight of ion-exchanged water and 450 parts by weight of
0.1 mol/L aqueous Na.sub.3PO.sub.4 solution were added to a 21-L
four-neck flask equipped with a high-speed stirrer, the revolution
speed was adjusted to 12,000 rpm, and the solution was heated to
65.degree. C. Then, 68 parts by weight of a 1.0 mol/L aqueous
CaCl.sub.2 solution was gradually added to prepare a dispersion
medium system including a small amount of Ca.sub.3(PO.sub.4).sub.2
as a sparingly water-soluble dispersing agent.
Meanwhile, the dispersoid system is as follows:
Styrene monomer: 165 parts by weight.
n-Butyl acrylate monomer: 35 parts by weight.
C.I. Pigment Blue 15:30:14 parts by weight.
Saturated polyester: 10 parts by weight.
{Acid value of terephthalic acid-propylene oxide modified bisphenol
A is 15, peak molecular weight: 6000.}
Salicylic acid metal compound: 2 parts by weight.
The following compound (maximum peak value: 59.4.degree. C.): 60
parts by weight.
##STR00005##
After dispersing the above mixture for 3 h by using an attritor, a
dispersion matter to which 10 parts by weight of
2,2'-azobis(2,4-dimethylvaleronitrile) as a polymerization
initiator was added was charged into the dispersion medium, and
granulation was carried out for 15 min while maintaining the
revolution speed. The stirrer was then changed from a high-speed
stirrer to a propeller stirring blade, the internal temperature was
raised to 80.degree. C., and polymerization was continued for 10 h
at 50 rpm. After completion of the polymerization, the slurry was
cooled and dilute hydrochloric acid was added to remove the
dispersion medium. After further washing and drying, the cyan toner
had a weight-average particle diameter (measured by Coulter
Counter) of 6.2 .mu.m, a number variation factor of 27%, and a SF-1
of 104.
A yellow toner, a magenta toner, and a black toner having a SF-1 of
104 were produced in the same manner. C.I. Pigment Yellow 17, C.I.
Pigment Red 122, and carbon black were used as colorants for the
yellow toner, magenta toner, and black toner, respectively.
FIG. 4 is a graph showing the results obtained in measuring the
relationship between the toner amount per unit surface area which
is developed on the photosensitive drum when the peripheral
velocity ratio, which is the ratio of the peripheral velocity of
the developing roller to the peripheral velocity of the
photosensitive drum, is changed. The potential setting of the
photosensitive drum, the developing roller bias, and the toner
charge quantity, and the like, are set as appropriate. As the
peripheral velocity ratio of the developing roller to the
photosensitive drum is increased from 100%, the amount of toner
developed on the photosensitive drum (moved from the developing
roller and placed on the photosensitive drum) increases, and the
toner amount is saturated at a peripheral velocity ratio of about
280%.
FIG. 5 is a graph showing the relationship between the toner amount
per unit surface area on the recording material and the reflection
density, the relationship being measured after transferring and
fixing the toner image developed on the photosensitive drum onto
the recording material. The reflection density was measured using a
reflection density measuring instrument Model RD-918 from
GretagMacbeth GmbH. FIG. 5 shows magenta (M) toner as an example of
YMCK. As the amount of toner on the recording material increases,
the reflection density increases and the reflection density reaches
saturation when the toner amount on the recording material is about
8E-03 [kg/m.sup.2].
From the above results, in the present example, the normal image
forming mode and the wide color gamut image forming mode were set
in the following manner. As the normal image forming mode, since it
is sufficient for a general office document, or the like, to have a
reflection density of about 1.45, the peripheral velocity ratio of
the photosensitive drum and the developing roller was set to 140%
and the maximum toner amount on the recording material was set to
about 4.0E-03 [kg/m.sup.2] in a single color. As the wide color
gamut image forming mode, the peripheral velocity ratio of the
photosensitive drum and the developing roller was set to 280% and
the maximum toner amount on the recording material was set to about
8.0E-03 [kg/m.sup.2] in a single color.
The following means was used to increase the peripheral velocity
ratio of the photosensitive drum and the developing roller to 280%
in the wide color gamut image forming mode with respect to the
peripheral velocity ratio of the photosensitive drum and the
developing roller of 140% in the normal image forming mode. When
the process speed in the normal image forming mode was taken as a
1/1 speed, in the wide color gamut image forming mode, the process
speed was set to a 1/2 speed, the peripheral velocity (revolution
speed) of the photosensitive drum was set to be half that in the
normal image forming mode, and the peripheral velocity (revolution
speed) of the developing roller was set to be the same as in the
normal image forming mode. For example, the peripheral velocity of
the developing roller is fixed at 0.28 [m/s], and the peripheral
velocity of the photosensitive drum is set to 0.2 [m/s] in the
normal image forming mode and to 0.1 [m/s] in the wide color gamut
image forming mode.
For example, it is also possible to increase the peripheral
velocity ratio of the photosensitive drum and the developing roller
to 280% by increasing the peripheral velocity (revolution speed) of
the developing roller by a factor of about two while maintaining
the process speed at a 1/1 speed. In this case, the load applied to
the driving motor as the driving source of the developing roller
becomes large, and it is necessary to increase the fixing
capability by raising the fixing temperature or the like. However,
the image forming time can be shortened with respect to a process
speed of a 1/2 speed. Meanwhile, where the process speed is set to
a 1/2 speed, the load applied to the driving motor of the
developing roller does not increase, and appropriate fixing is
possible even without increasing the fixing temperature.
Accordingly, in the present example, the setting for lowering the
process speed is selected in the wide color gamut image forming
mode.
FIG. 6 is a block diagram showing an example of the configuration
of the controller of the image forming apparatus according to the
present example. From a host PC 601, a print job generally
described in a page description language (PDL) such as PCL or
PostScript is sent to a video controller 602 of the image forming
apparatus. The video controller 602 as a conversion portion in the
present example mainly includes a raster image processor (RIP)
portion 604, a color conversion portion 605, a .gamma. correction
portion 606, and a halftoning portion 607.
The RIP portion 604 performs file analysis (interpreting) of a
print job described by PDL sent from the host PC 601 and performs
bitmap data conversion of RGB corresponding to the resolution (for
example, 600 dpi) of the image forming apparatus.
The color conversion portion 605 performs conversion such as to
match the tinges as much as possible in consideration of
differences in color reproduction ranges between the devices and
also match the appearance of colors, and further converts RGB into
color data YMCK of the developers (toners). The color conversion
portion 605 includes a color matching portion 608 that performs
color matching between devices, and a color separation portion 609
that converts the color-matched color space data into toner data
YMCK of respective colors of the image forming apparatus.
Generally, when a file created while watching a liquid crystal
monitor with an application (image software, office suite software,
etc.) on a computer is printed by an image forming apparatus, the
color reproduction range (R'G'B') of the image forming apparatus is
narrower than the color reproduction range (RGB) of the liquid
crystal monitor. With consideration for this difference in color
gamut between an input device (an image display device such as a
liquid crystal monitor) and an output device (an
electrophotographic printer or the like), the color matching
portion 608 is used to perform color matching conversion such as to
match the tinges as much as possible and also match the appearance
of colors. The color separation portion 609 converts the R'G'B'
which has been color-matched by the color matching portion 608 into
color data YMCK of each developer.
The image data of each color of YMCK which have been converted and
generated by the color separation portion 609 are gamma-corrected
with the .gamma. correction portion 606. The image data of each
color of YMCK which have been gamma-corrected with the .gamma.
correction portion 606 are subjected to gradation expression
processing such as dithering with the halftoning portion 607, and a
signal is sent to the image forming engine controller.
The present invention is characterized in that the way by which
image data are converted in the color matching portion 608, the
color separation portion 609, the .gamma. correction portion 606,
and the halftoning portion 607 changes in accordance with the image
forming mode. As an example thereof, in the present example, the
case is explained in which the conversion condition of gamma
correction as an image formation condition is caused to differ
between the normal image forming mode and the wide color gamut
image forming mode. However, the present invention is not limited
to this example, and an image may be converted by taking the
conversion condition of the color matching portion 608 as a first
conversion condition in the normal image forming mode and as a
second conversion condition in the wide color gamut image forming
mode. Depending on the configuration, the gamma correction process
may be omitted.
FIG. 7 is an explanatory diagram illustrating .gamma. correction of
image formation conditions in the normal image forming mode in the
present example. The upper left graph in FIG. 7 is an original
.gamma. curve 1 showing the gradation characteristic in the case
where an image (recorded image) is formed on the recording material
by directly using the image data of the YMCK color expression
converted from the image data of the RBG color expression in the
color separation portion 609. Since the original .gamma. curve 1 is
not linear with respect to the image data, .gamma. correction is
performed to make it linear. The .gamma. correction is performed
using a look-up table (LUT). By performing the .gamma. correction,
it is possible to obtain a linear gradation characteristic of the
image (recorded image) formed on the recording material. Therefore,
as shown by the corrected .gamma. curve 1, the relationship between
the input image data (first image data) and the reflection density
of the image formed on the recording material shows a linear
gradation characteristic of the image formed in the recorded
image.
For example, where it is desired to obtain a reflection density of
0.8 with respect to image data 80h, it follows from the original
.gamma. curve 1 that A0h can be used as image data to be actually
used on the image forming apparatus side in order to obtain the
reflection density of 0.8. The image data to be used correspond to
converted second image data. Therefore, an association is
established such as to use A0h as actual image data to be received
on the image forming apparatus side when the input image data are
80h. A LUT is created by likewise associating a series of input
image data with image data to be actually used. The LUT created in
this way is a LUT 1 shown in the upper right graph in FIG. 7. As a
result of using this LUT 1, the corrected .gamma. curve 1 becomes
linear as shown in the lower left graph in FIG. 7.
FIG. 8 is a diagram illustrating the case where the LUT 1 in the
normal image forming mode is used as is in the wide color gamut
image forming mode as a conventional example. In the wide color
gamut image forming mode, the amount of toner placed per unit
surface area on the recording material (a laid-on level of the
developer per unit area of the recording material) is increased.
Therefore, the original .gamma. curve 2 showing the gradation
characteristic in the case where image formation is performed by
using as is the image data of YMCK color representation, which have
been converted from image data of RGB color representation in the
color separation portion 609 in the wide color gamut image forming
mode, becomes as an upper left graph in FIG. 8. A broken line is
the original .gamma. curve 1 in the normal image forming mode.
As shown in the upper left section of FIG. 8, the original .gamma.
curve 2 in the wide color gamut image forming mode shows a
gradation characteristic with a reflection density greater than
that of the original .gamma. curve 1 in the normal image forming
mode over the entire gradation characteristic (from a minimum
density of 00h to a maximum density of FFh). Therefore, where
.gamma. correction is performed using the LUT 1 in the normal image
forming mode, for example, since the input image data are corrected
to 80h so that the image data actually used in the LUT 1 become
A0h, the density becomes as high as 1.2 in the original .gamma.
curve 2. Also, the corrected .gamma. curve becomes nonlinear. For
this reason, it is possible that the overall density will increase,
the gradation of the image will be lost, or the appearance of color
will change.
FIG. 9 is a diagram for explaining the case where an image
formation condition different from the image formation condition in
the normal image forming mode is used in the wide color gamut image
forming mode in the present example. The present invention is
characterized in that an image formation condition different from
the image formation condition in the normal image forming mode is
used in the wide color gamut image forming mode. In the present
example, as an image formation condition different from that in the
normal image forming mode, a LUT 2 which is different from the LUT
1 used in the normal image forming mode is used as a LUT that
defines the conversion condition of image data in .gamma.
correction.
The LUT 1 is a LUT in which the entire gradation characteristic of
the image outputted to the recording material in the normal image
forming mode shows linear gradation of an image. Thus, this is a
LUT in which image data (output image data) to be actually used are
allocated with respect to the original image data (input image
data) so as to show a linear gradation characteristic over the
entire density range from the minimum density 00h to the maximum
density FFh. The gradation characteristic of the image data to be
outputted to the recording material which is obtained with the LUT
1 corresponds to the first gradation characteristic in the present
example. The conversion condition defining the association between
the input image data and the output image data such as to realize
this gradation characteristic corresponds to the first conversion
condition in the present example.
In the present example, the LUT 2 can be exemplified by a LUT in
which input image data and output image data are associated so that
the color gamut widens in a high-density region (second density
region) which is close to a solid region so that the corrected
.gamma. curve becomes the same as the corrected .gamma. curve in
the normal image forming mode in the middle- and low-density
regions (first density region). Thus, from 00h to 60h and from 61h
to C7h (low- and medium-density regions), a linear gradation
characteristic (constant density increase rate until FFh=1.45) is
shown in the case in which the maximum density (reflection density
at FFh) is made the same as the maximum density (1.45) in the
normal image forming mode. Further, from C8h to ffh (high-density
region), gradation of an image is shown such that the density
increase rate gradually increases with respect to the constant
density increase rate in the middle- and low-density regions. The
gradation characteristic obtained with the LUT 2 corresponds to the
second gradation characteristic in the present invention, and the
conversion condition defining the association between the input
image data and the output image data corresponds to the second
conversion condition in the present invention so as to realize such
a gradation characteristic. As a result, it is possible to widen
the color gamut while ensuring the gradation of a halftone image in
the wide color gamut image forming mode.
FIG. 10 is a chromaticity diagram illustrating the comparison
between the color gamut in the case of forming a color image in the
normal image forming mode and the color gamut in the case of
forming a color image in the wide color gamut image forming mode in
the present example. The broken line is the color gamut in the
normal image forming mode, and the solid line is the color gamut in
the wide image forming mode. A L*a*b* colorimetric system (CIE) was
used to evaluate the color gamut. An L axis in the L*a*b*
colorimetric system (CIE) is the axis perpendicular to the paper
plane in FIG. 10, and only an a axis and a b axis are shown in FIG.
10. The same applies to FIGS. 11 and 12. The chromaticity was
measured using Spectordensitometer 500 manufactured by X-Rite Inc.
FIG. 10 shows changes in color gamut when the control in the wide
color gamut image forming mode of the present invention is
implemented in the same way in the process cartridges of yellow
(Y), magenta (M), and cyan (C) colors which are basic colors in
color image formation. It is clear that as a result of switching
from the normal image forming mode to the wide color gamut image
forming mode, for example, the color gamut of red (R) formed by
yellow (Y) and magenta (M) and the color gamut of green (G) formed
by yellow (Y) and cyan (C) are enlarged. For yellow (Y) and red
(R), the color gamut can be enlarged from 5% to 15%. For the wide
color gamut image forming mode, the present invention can be also
applied to the case where only the color gamut of a specific tinge
is enlarged. For example, when enlarging only the color gamut of
blue (B) formed by magenta (M) and cyan (C), the wide color gamut
image forming mode may be implemented only for the magenta and cyan
process cartridges among the four process cartridges.
EXAMPLE 2
An image forming apparatus according to Example 2 of the present
invention will be described hereinbelow with reference to FIGS. 11
and 12. In Example 2, components which are the same as in Example 1
are assigned with the same reference numerals as in Example 1, and
the explanation thereof is herein omitted. Matters not described
herein in Example 2 are the same as those in Example 1. Example 2
is characterized in that the color matching conversion table which
is used for processing in the color matching portion 608 of the
color conversion portion 605 is switched between the normal image
forming mode and the wide color gamut image forming mode as the
image formation condition.
FIG. 11 is a diagram showing how the color gamut range of RGB color
expression is changed by color matching conversion in the normal
image forming mode in the present example. The broken line
indicates the color reproduction range (for example, sRGB) of a
liquid crystal monitor which is an input device. Meanwhile, the
solid line indicates the color reproduction range of the output
image of the image forming apparatus which is an output device, and
corresponds to the first color reproduction range in the present
invention. The color reproduction range of the electrophotographic
output image is narrower than the color reproduction range of the
input device. Therefore, the RGB values of the input device color
space are converted into R'G'B' values which have been
color-matched to the output device color space. In other words, in
many cases, the ratio of each color of RGB, when displaying a
predetermined color in the input device, cannot be used as is when
outputting with the output device because of the difference in
color gamut range between the input device and the output device.
Accordingly, the ratio of RGB constituting the predetermined color
on the input device and the ratio of R'G'B' constituting the
predetermined color to be outputted by the output device are
associated for each outputable color, as indicated by the following
equation, and the table in which the conversion conditions are
summarized is a color matching conversion table.
'''.function..times. ##EQU00002##
Next, color matching conversion in the wide color gamut image
forming mode will be explained. Where the color matching conversion
table used in the wide color gamut image forming mode is the same
as that in the normal image forming mode, as in the related art,
since the color gamut is changed to the same color gamut, the color
gamut cannot be widened. By contrast, the present example is
characterized in that a color matching conversion table different
from the color matching conversion table in the normal image
forming mode is used in the wide color gamut image forming
mode.
FIG. 12 is a diagram showing how the color gamut range of RGB color
expression is changed by color matching conversion in the wide
color gamut image forming mode in the present example. The broken
line indicates the RGB color space of the input device, the one-dot
broken line indicates the R'G'B' color space in the normal image
forming mode, and the solid line indicates the R'G'B' color space
in the wide color gamut image forming mode. The color reproduction
range indicated by the solid line corresponds to the second color
reproduction range in the present invention. As shown in FIG. 12,
since the R'G'B' color space in the wide color gamut image forming
mode is made wider than that in the normal image forming mode, the
color gamut can be widened. Color matching conversion in the normal
image forming mode is performed in the following manner. The
association (color matching conversion) between the RGB color space
and the R'G'B' color space is performed such as to obtain the
appearance of colors which is as uniform as possible. Further,
since the RGB color space is wider than the R'G'B' color space, a
region outside the R'G'B' color space is closely associated with
the outer peripheral edge region of the R'G'B' color space. By
contrast, since the color matching conversion in the wide color
gamut image forming mode performs association to the R'G'B' color
space which is wider than that in the normal image forming mode,
the reproducible tinges are further increased. As a result, the
appearance of colors can be better matched. Further, with respect
to a region outside of the R'G'B' color space, the association with
the outer peripheral edge region of the R'G'B' color space can be
performed more sparsely than in the normal image forming mode. As a
result, a more natural appearance of colors can be obtained. The
effect obtained in Example 2 which is different from those obtained
in Example 1 is that the appearance of colors can be matched as
much as possible.
EXAMPLE 3
An image forming apparatus according to Example 3 of the present
invention will be described hereinbelow with reference to FIG. 13.
In Example 3, components which are the same as in Examples 1 and 2
are assigned with the same reference numerals as in Examples 1 and
2, and the explanation thereof is herein omitted. Matters not
described herein in Example 3 are the same as those in Examples 1
and 2. In Examples 1 and 2, the user designates, by using an
operation panel (not shown in the drawing) of the image forming
apparatus 200 or a host PC, whether the image forming mode is to be
set to the normal image forming mode or the wide color gamut image
forming mode. By contrast, in Example 3, the configuration is used
in which the image forming apparatus 200 can designate the image
forming mode by itself.
In the present example, the engine controller 603 determines
whether the image for which image formation has been designated to
be performed is the normal image to be outputted in the normal
image forming mode or a wide color gamut image to be outputted in
the wide color gamut image forming mode, as wide color gamut image
determining means. The determination is made on the basis of
whether image data of the image for which image formation has been
designated are normal image data as non-wide-color-gamut image
data, or wide color gamut image data. Non-wide-color-gamut image
data are image data composed only of dot data with a density less
than a predetermined threshold, and are data that can be outputted
with sufficient color expression in the normal image forming mode.
The wide color gamut image data are image data including dot data
with a density equal to or greater than the predetermined threshold
value, and are data that need to be outputted in the wide color
gamut image forming mode because they cannot be sufficiently
color-expressed in the normal image forming mode.
The engine controller 603 automatically switches the operation mode
to the normal image forming mode or the wide color gamut image
forming mode according to the determination result and performs
image formation under the image formation condition corresponding
to the respective image forming mode. Here, it may be also
preferable to switch the modes with the engine controller 603 in
preference to mode designation by the user. For example, in some
cases, although the user has designated the wide color gamut image
forming mode, the image data thereof are image data that can be
outputted in the color gamut range in the normal image forming
mode. In this case, it is possible to improve productivity by
outputting in the normal image forming mode rather than outputting
in the wide color gamut image forming mode in which more time is
required till the output because of the change in the peripheral
velocity ratio.
FIG. 13 is a flowchart showing the flow of automatic selection
control of the image forming mode at the time of the image forming
operation of Example 3 of the present invention. According to the
flowchart shown in FIG. 13, the engine controller 603 selects the
image forming mode, sets the image formation condition, and causes
the image forming apparatus 200 to execute the image forming
operation. First, where the image forming operation mode designated
by the user is not the wide color gamut image forming mode (S301,
No), that is, where the user designates the normal image forming
mode, the engine controller 603 selects the normal image forming
mode (S302). Then, the engine controller 603 selects .gamma.
correction or color matching conversion table as the image
formation condition for the normal image forming mode, which has
been described in Examples 1 and 2, as the image formation
condition (S303), and performs correction, or the like, of the
predetermined image data to form an image (S304).
In the configuration of the present example, when the user selects
the normal image forming mode, the contents of the image data to be
outputted are not verified, that is, it is not determined whether
the image data are of the normal image or of the wide color gamut
image. This is because even when the original image data are wide
color gamut data, the user does not necessarily obtain the image
output in the wide color gamut. A configuration different from that
of the present example may be also used in which even when the user
selects the normal image forming mode, an image forming mode
suitable for the contents of the image data is automatically
selected.
When the image forming operation mode designated by the user is the
wide color gamut image forming mode (S301, Yes), it is determined
whether the image data to be outputted are image data of a normal
image or image data of a wide color gamut image (S305). Where the
image data are image data of a normal image (S305, No), the normal
image forming mode is selected (S302), and image formation in the
normal image forming mode is executed (S303, S304). Meanwhile,
where the image data are image data of a wide color gamut image
(S305, Yes), the wide color gamut image forming mode is selected
(S306), the image formation condition for the wide color gamut
image forming mode is selected (S307), and image formation is
performed (S304).
The determination of the image data may be based on the state of
RGB image data. For example, in the case of 8-bit data of each
color of RGB, where dot data of C8h or more are present in any of
the color data, the image is determined to be a wide color gamut
image. When color data are composed only of dot data less than C8h,
the image is determined to be a normal image. After the
determination, the operation is performed in the image forming mode
corresponding to the determination result, and the image formation
is performed under the image formation condition corresponding to
the image forming mode.
Alternatively, the image determination may be performed with YMCK
data after conversion from RGB to YMCK data. For example, when each
color of YMCK is set to 8-bit data, where dot data of C8h or more
are included in any of the color data, the image is determined to
be a wide color gamut image. When color data are all composed only
of dot data less than C8h, the image is determined to be a normal
image.
In the present example, the threshold value was set to C8h from the
viewpoint of whether or not the image data in a high density region
(C8h to FFh) in the present example are included in the color data,
but the determination threshold is not limited to the
aforementioned C8h and may be set appropriately.
According to the present example, when the wide color gamut image
forming mode is designated and the actual print image is a normal
image which inherently does not necessarily require image formation
in the wide color gamut, the decrease in the productivity of the
print caused by operation in the wide color gamut image forming
mode can be prevented.
In the above-described examples, the case is explained in which the
image forming apparatus itself has the configuration such that
final image data to be used for image formation are generated by
processing, e.g., .gamma. correcting, the original image data, but
configurations to which the present invention can be applied are
not limited to the aforementioned configuration. For example, in an
image forming system including an image forming apparatus, a host
CPU, and other peripherals such as a display, the present invention
can be also applied to a configuration in which the host CPU
functions as a data generating device for performing processing and
generation, such as correction, of the image data.
While the present invention has been described with reference to
exemplary embodiments, it is to be understood that the invention is
not limited to the disclosed exemplary embodiments. The scope of
the following claims is to be accorded the broadest interpretation
so as to encompass all such modifications and equivalent structures
and functions.
This application claims the benefit of Japanese Patent Application
No. 2016-072514, filed on Mar. 31, 2016, which is hereby
incorporated by reference herein in its entirety.
* * * * *